Agency's Tax-Exempt Unit Faulted in Past Reports by Its Watchdog

The Internal Revenue Service unit under scrutiny for targeting conservative groups has been faulted previously by the Treasury Department's inspector general for an array of problems, from delayed processing of files to chronic understaffing to inadequate training.

Five inspector-general reports from 2005 to 2012 didn't find indications of political bias, but they detailed a litany of shortcomings in the way the IRS's Exempt...